Systems that provide for the collection of handwritten signatures on electronically delivered documents are in common use. A sensor panel, such as a resistive or capacitive type, is provided for a signer. When the sensor panel is traversed by a stylus in a handwriting transaction, the sensor panel outputs X-Y coordinate data derived from a voltage gradient on the panel corresponding to the handwritten signature scribed thereon. A controller utilizes the X-Y coordinate data from the stylus to record the location of the stylus on the sensor panel at regular intervals as digital signature data. The signature data contains the path of the pen as a progression of coordinate sets that, when charted, provides a virtual map of the signature.
The coordinate-set information of the digitized signature data may then be further processed. For example, signature devices that employ a Universal Serial Bus (USB) interface may be configured to transmit signature data as X-Y coordinates through proprietary or standard USB Human Interface Device (HID) “reports” or “packets,” i.e., data having a predetermined structure so that a host device may be configured accordingly to receive the data.
Some signature-capture devices are configured to generate and transmit signatures as rasterized images. The images are compressed using one or more raster compression techniques common to the format of the raster chosen. An advantage of raster images is that many formats are ubiquitous and relatively easy to work with because there are many tools available in the art to encode and decode them. However, a disadvantage of raster images of signatures is that, even when compressed, they tend to require relatively large electronic files because they describe a plethora of pixels rather than the relatively small number of vectors required to describe the strokes of a signature. In addition, raster images do not scale well; scaling up causes signatures to become pixilated and thus poor-quality, while scaling down irreversibly removes data from the signature. Yet another disadvantage of raster signatures is that there is no timing information, which is desirable for forensic analysis. Another concern is that digitized signatures often must be stored in electronic databases. Due to their relatively large file size, storing raster images is not desirable since a correspondingly large amount of storage capacity must be provided.
Given the shortcomings of raster images it is desirable to transmit signatures over a USB keyboard interface, and to do so efficiently. U.S. patent application Ser. No. 13/771,843, filed Feb. 20, 2013 and incorporated by reference herein, is commonly owned by the applicant of the present invention and discloses a system configured to encode signature data as a series of keystrokes that can be interpreted by a host. One drawback of this arrangement is that computer operating systems such as Windows, OSX, and Linux poll the keyboard on a regular basis. Consequently, the amount of keystrokes that can be transmitted is limited by the poll rate of the operating system. When the operating system polls the keyboard and finds keystrokes it places them into a buffer. The buffer is emptied asynchronously. It is therefore possible for the buffer to overflow, resulting in undesirable data loss.
Another problem with USB keyboard interfaces is that after the signature is received by the host computer it is sometimes necessary to transmit that signature over a relatively slow interface, such as a 2400 baud modem. If the signature data includes a large number of keystrokes the amount of time required to transmit the message may be unacceptable. In addition, if buffers are utilized they may overflow, resulting in unacceptable loss of data.